Fish raised in aquaculture production can cause serious harm when unintentionally or intentionally released from aquaculture facilities. Escaped fish can harm wild fish populations, other species and the ecosystem. And the problem is not a hypothetical one. Upwards of 10 million Chilean farmed salmon reportedly escape each year.
Fish in open net pens escape in small numbers even during normal operations and can escape in large quantities when nets are damaged by storms or predators, such as sharks and sea lions. Atlantic salmon escapes on the U.S. and Canadian west coasts are common; there were 350,000 known escapes in 1997 and farmed Atlantic salmon have been found thousands of miles away from the closest salmon aquaculture facilities.
In the Pacific Ocean, escaped non-native Atlantic salmon have been found breeding near aquaculture operations in both British Columbia and South America. Escapes are a significant concern because they occur on a regular basis. Escaped fish have been known to travel great distances and they are a threat to the long-term health and fitness of native populations.
Wild fish are threatened by a potentially endless rain of escapes – fertilized eggs and larvae – that easily drift away from a net with mesh that is many times larger than these tiny young fish. While efforts have been made to sterilize captive fish, those efforts are not 100 percent effective. Like introductions of non-native adult fish, larval introductions become invasive species.
Unavoidable natural disasters can also result in fish escapes. In April 2007, an earthquake in Chile measuring 6.2 on the Richter scale resulted in a massive escape of net pen-raised salmon. The earthquake killed several workers and resulted in an estimated 12 million escaped salmon.